1. Field of the Invention
The present invention relates generally to electrical wiring devices, and particularly to electrical wiring devices having safety features.
2. Technical Background
The AC power interface for the typical electrical distribution system is commonly known as the breaker panel. The size of the breaker panel may vary depending on whether it is disposed within a residence, commercial building or some other such facility. The breaker panel, of course, terminates the AC power service provided by the power utility and distributes AC power to one or more branch electric circuits installed in the structure. Branch electric circuits often include one or more electrical wiring devices, such as receptacle outlets, that accommodate electrical power plugs.
Electrical wiring devices are provided in electrically non-conductive housings. The housing includes electrical line terminals that are electrically insulated from electrical load terminals. The line terminals connect the wiring device to conductive wires from the breaker panel. Load terminals are connected to downstream wiring that is configured to propagate AC power to one or more downstream electrical loads. Those of ordinary skill in the pertinent art will understand that the term “load” refers to an appliance, a switch, or some other electrically powered device. The load terminals of an electrical wiring device are sometimes referred to as “feed-through” terminals. As alluded to above, the AC power propagating through a device may be accessed by the user by way of a power plug. As everyone knows, the power plug and cord assembly for a portable electrical device functions as a portable device's AC power interface. A receptacle outlet provide power to portable “user-accessible loads” when the plug is inserted into a receptacle outlet. Certain types of faults are known to occur in branch electric circuits and electrical wiring systems. These faults represent serious safety issues that may result in fire, shock or electrocution if not addressed properly.
Accordingly, branch electric circuits typically employ one or more electric circuit protection devices. Protective devices employ a circuit interrupter disposed between the line terminals and the load terminals. The circuit interrupter provides power to the load terminals under normal conditions, but breaks electrical connectivity when the protective device detects a fault condition in the load circuit. There are several types of electric circuit protection devices including ground fault circuit interrupters (GFCIs), ground-fault equipment protectors (GFEPs), arc fault circuit interrupters (AFCIs), transient voltage surge suppressors (TVSSs), or surge protective devices (SPDs). This list includes representative examples and is not meant to be exhaustive. Some devices include both GFCIs and AFCIs. As their names suggest, arc fault circuit interrupters (AFCIs), ground-fault equipment protectors (GFEPs) ground fault circuit interrupters (GFCIs), transient voltage surge suppressors (TVSSs), or surge protective devices (SPD's) perform different functions. Electric circuit protective devices may be disposed within a circuit breaker that provides overcurrent protection, receptacle outlets, plugs, etc. Portable electrical wiring devices, e.g., hair dryers, etc., may also have a protective device disposed therein.
Another safety issue that is of great concern relates to the amount of ambient lighting in a given room or space. In a scenario that most people are familiar with, a person entering a darkened room will usually attempt to locate the wall switch and turn the wall switch to the ON position before entering. Sometimes the wall switch is not located near the door, i.e., at the point of entry, and the person will begin to search for the light switch. This person begins to “feel” her way around the darkened room in an attempt to navigate around objects such as tables and chairs. More often than not, the person successfully finds the wall switch and manages to turn the lights ON. On the other hand, the darkened room represents a safety issue. For example, if an object is disposed relatively low to the floor surface the person may trip over it and suffer an injury. This scenario applies to other types of spaces, such as corridors, theater aisles, stairways, patios, garages, ingress/egress areas, out-buildings, outdoor pathways and the like.
There are situations where a light switch is not available, or is not readily available. There are other situations where the person entering the darkened room is disinclined to turn the lights ON as a matter of courtesy. Several examples immediately come to mind. A person entering a darkened theatre would expect to incur the wrath of his fellow patrons if he turned the theatre lights ON while finding a seat. In another situation, a person may desire to temporarily enter a room occupied by a person who is sleeping. For example, a parent may want to check on the condition of a sleeping infant, or tend to someone who is ill, without having to turn the lights ON.
In one approach that has been considered, a portable lighting device may be inserted into an electrical receptacle located in the room to function as a “night light.” While this arrangement may provide a temporarily solution to the potentially unsafe condition described above, it has certain drawbacks associated with it. The most obvious drawback in getting the portable nightlight into a socket in a darkened room is finding the socket in the first place. While this problem may be eliminated with forethought, many people live busy lives and have other things on their minds. On the other hand, once the night light is inserted into the receptacle, it may remain there day and night for an extended period of time and represent a waste of energy. After awhile, the resident may notice the problem and unplug the light during daylight hours if the space admits natural light. Unfortunately, the resident may forget to plug the light back into the socket until after night fall and finds himself revisiting the darkened room scenario. In addition, once a small night light is unplugged from the receptacle there is the possibility that it will become lost, misplaced, or damaged from excessive handling.
In another approach that has been considered, a light element may be disposed in a wiring device in combination with another functional element such as a receptacle or a light switch. The wiring device is subsequently installed in a wall box or mounted to a panel. While this approach obviates some of the drawbacks described above, there are other drawbacks that come into play. Conventional permanent lighting elements such as incandescent and neon lights have a relatively short life expectancy of only a few years and, therefore, require periodic servicing and/or replacement. This problem is exacerbated by the fact that the light is typically hard-wired to power contacts disposed in the wiring device. As such, the light element is permanently ON, further limiting the light elements life expectancy of the device.
In yet another approach that has been considered, the aforementioned drawbacks are addressed by providing a light sensor, and the associated circuitry, to control the light element. When the sensor detects the ambient light level falling past a certain point, the control circuit turns the light element ON. One design problem associated with using a light sensor to selectively actuate the light element relates to providing a proper degree of isolation between the light sensor and the light element. Conventional devices solve the problem by separating the light sensor and the light element by as great a distance as possible. As such, conventional devices are typically arranged such that the lens covering the light element is disposed in one portion of the wiring device cover and the sensor element is disposed in a second portion of the cover, with sufficient space therebetween. If the wiring device includes another functional element such as a receptacle, the sensor may be disposed between the receptacle and the light's lens cover. Because the light sensor must be disposed a sufficient distance away from the light element, it necessarily requires that the lighting assembly be reduced in size to fit the wiring device form factor. Accordingly, conventional devices of this type often fail to provide an adequate amount of illumination for the intended application and, therefore, do not address the safety concern in a satisfactory manner.
What is needed is an electrical wiring device that includes a light source that is both adapted to a wiring device form factor and configured to address the drawbacks and needs described above. A light emitting wiring device is needed that provides a sufficient amount of illumination when the ambient light in a given space falls below a safe level. The wiring device must maximize the effective area of illumination without sacrificing sensor isolation. What is also needed is a wiring device that addresses both safety issues, i.e., electrical fault conditions as well as ambient lighting issues.